For the production of stuffed meat products, animal intestines have been use since time immemorial as the containers. The manufactured products introduced in these casings are then subjected to various processes (cooking, fermentation . . . ) until the end food product is produced.
On the other hand, natural casings have been imitated by humans, which has given rise to the production of artificial casings. Artificial casings are tubular wrappers of very defined characteristics, which are designed for the production of food, such as, for example sausages, salami and large variety of stuffed meat products.
Artificial casings are produced of plastic material (for example, polyamides), as well as cellulose-based casings, either alone or with the reinforcement of a fibrous paper, which acts as mould for the manufacturing of the stuffed meat products with a defined diameter, as well as container for its transport and it can even have a drawing or the manufacturer's brand printed thereon. These artificial casings cannot be ingested together with the stuffed meat product and should be peeled off before final consumption.
Other artificial casings are even prepared from edible material, such as collagen extracted from cows or pigs, and give rise to casings which can be consumed together with the rest of the stuffed meat product, in a similar form to stuffed meat products produced with natural casings.
Although in some cases, especially in high-calibre casings, the casings are offered in individual portions designed for the stuffing of a food item or in balls designed for the manufacturing of a reduced number of food items, artificial casings are usually subjected to a special process called “pleating” before its sale.
In this pleating process, the casing is creased in an orderly fashion like the folds of an accordion, forming pleated tubular wrappers (called “pleated wrappings”) which provide large lengths of casings in a form easy to stuff in modern automatic machines such as those disclosed in U.S. Pat. No. 3,115,668 Townsend. This pleating process and an example of its application are disclosed, for example, in U.S. Pat. No. 2,983,949 Matecki and U.S. Pat. No. 5,782,83 Stall.
During the pleating process, it is typical to add different natural substances to the casing, such as a small amount of oil to lubricate it and for it to resist the pleating process without tearing, or an interior spray which can carry different substances, such as wetting agents, e.g. water, glycerine, or agents which contribute to the subsequent easy peeling of the casing from the rest of the stuffed meat product.
The pleating process forms a series of folds in the casing similar to those of an accordion which generally follow an ordered pattern, the form of these folding patterns being the object of several patents, such as U.S. Pat. No. 3,907,003 and U.S. Pat. No. 3,988,804 (Regner) and U.S. Pat. No. 4,210,981, since they have great effect on the quantity of casing that can be compressed in a determined length of pleated wrapper, as well as the stability of the wrapper produced and in its later functioning (height and uniform interior diameters of the pleated wrapper which ensure the problem-free stuffing and uniform strength of resistance to unpleating of the casing during its stuffing).
Generally, when the casing is unpleated, creases from the folds made during the pleating process are observed. Although these folds may previously have been irregular, pleating techniques have evolved to provide a very regular and homogenous pleating process, which means that it is typical that these folds occur with a very repetitive structure. Generally, in the most typical pleating types, a helicoidal crease throughout the casing is usually observed in the casing when unpleated, which is typically known as “major or primary spiral”, resulting from the main fold which extends towards the outside of the pleated wrapper, and a series of accessory creases of various forms which are called “secondary folds”, interspersed between the major spiral and the interior diameter of the pleated wrapper, and which are disclosed, for example, in U.S. Pat. No. 3,907,003 and U.S. Pat. No. 4,210,981.
Casings are also known in the state of the art which can transfer colour to the stuffed meat product produced with them, as is the case of U.S. Pat. No. 2,521,101 (Thor) or US2003/0039724 A1 (Viskase).
Other casings contain a caramel colouring agent which gives a pleasant brown tone to the sausage surface, such as those disclosed in U.S. Pat. No. 3,860,728 or WO 2004/094544 A1 (Teepak).
Other casings contain a product which develops its brown colour by reaction on being subjected to high temperatures as disclosed in U.S. Pat. No. 5,270,067 (Underwood).
There are numerous patents (such as U.S. Pat. No. 4,657,765 Viskase, U.S. Pat. No. 6,032,701 Teepak) designed for the production of casings which transfer liquid smoke to the sausage surfaces, and which replace the need for the smoking step in sausage manufacture.
The impregnation process of the casing with the liquid smoke solution can be carried out in several forms well known in the state of the art, such as those stated in U.S. Pat. No. 4,518,619 (Chiu), thus, the casing can pass through a bath which impregnates it, the liquid smoke can be added by spraying during the pleating process of the casing, or the solution can be introduced in the interior of the casing which is made to slide between rollers (“bubble coating”).
U.S. Pat. No. 4,504,500 (Red Arrow) also discloses an impregnation method with liquid smoke of a pleated casing wrapper, wherein the pleated wrapper is placed in contact with the liquid smoke solution, and a differential pressure is applied which forces the flow between the folds of the casing until essentially the entire surface of the casing is uniformly impregnated with the liquid smoke.
Casing impregnation processes (essentially of humidity) are also known, wherein the casing is placed in contact with absorbent and resilient materials such as sponges, such as, for example, in U.S. Pat. No. 3,809,576 and U.S. Pat. No. 4,356,218.
It should be highlighted that, in general, in casings which are impregnated with substances designed to produce a surface colour on the surface of the stuffed meat products, it is aimed that this colour is homogenous, and when lines or marks appear at times, for example, associated to folds of the casing (caused during the production or pleating of the casing), said inhomogeneities are considered defects, as cited in US2003/0039724 A1 (paragraph [0035]) or in U.S. Pat. No. 4,818,551 (Col. 3, Line 10-16; Col. 7, Line 52-65), and although it is known that the pleating folds, if the casing impregnation is inhomogenous, can leave marks on the sausage, this phenomenon, however, although known, has not been advantageously used.
On the other hand, casings are known in the state of the art which can carry a determined drawing or pattern which will then hold the stuffed meat product, such as, for example, U.S. Pat. No. 3,961,082 by Naturin of printed edible collagen.
In U.S. Pat. No. 6,200,510 B1 a spray is applied on the casing in a step prior to its drying (it simulates stripes on the casing which are added before the casing pleating process).
Another technique permits leaving a logo or drawing on the sausage surface as it acts as a screen (mask) to the smoke used in the smoking process, of the logo or drawing printed on the casing with a special composition which is largely impermeable to smoke, as disclosed in U.S. Pat. No. 5,834,076 (Viscofan).
The object of several patents has also been the printing of cellulose casings with logos or marks, especially grill marks, which are transferred to the sausage surface during the cooking process, as disclosed in U.S. Pat. No. 5,084,283 and U.S. Pat. No. 5,085,890 (Viskase). However, this process is complex and entails the expense of an additional printing process and the need to turn the casing inside out during the pleating process, which makes it of little practical use.
In the cooking of heat treated meat products, typically dark coloured marks, called grill-type marks, are produced on their surface, due to the combination of high temperatures on the wires and contact with the food product. These grill-type marks usually follow a typical pattern, which characterizes the appearance of many meat products and are very attractive for the consumer.
The production of grill-type marks on foodstuffs is the object of several patents, such as:
U.S. Pat. No. 4,384,006 with hot wires which come into contact with the food once it advances and rotates, to form an uninterrupted spiral mark on the sausage surface.
U.S. Pat. No. 4,905,587 (Conagra) applies a fine layer of liquid to the meat during its stuffing in the casing, and comments (in column 4, line 65), that it can be adapted to produce grill-type marks.
U.S. Pat. No. 5,762,968 applies a spray of marks imitating grill-type marks, on food products.
Patent application US 2005/0008742 A1 and its equivalent WO 2005/006889 A1 (Red Arrow) provide a method of marking different foods, using jets of colouring solutions which produce marks on the food similar to grill-type marks, and whose colour is developed after the food is subject to a heat treatment.